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671.
长江中游地区第四纪河湖演变及其对环境的影响 总被引:8,自引:1,他引:8
第四纪以来,区内长江水系的演化和变迁经过了4个阶段,形成了丰富的资源,同时也是区内主要环境地质问题产生的根本原因,未来演变的趋势是湖群的进一步衰亡和荆江河段地上河继续抬升,这对区内环境潜伏着巨大威胁。 相似文献
672.
Trace element chemistry of major rivers in Orissa State, India 总被引:1,自引:1,他引:1
K. O. Konhauser M. A. Powell W. S. Fyfe F. J. Longstaffe S. Tripathy 《Environmental Geology》1997,29(1-2):132-141
Geochemical analyses of surface waters from rivers flowing through Orissa State, India, indicated that trace element concentrations
were extremely variable and consistently higher than world river average. The Brahmani River was the most solute-rich river
studied, followed by the Baitarani and Mahanadi Rivers. Although all three rivers drain similar geology, the Brahmani River
catchment is heavily industrialized, and water samples collected upstream and downstream from industries indicated that anthropogenic
activity directly influenced its chemical composition. Samples collected from several towns, in all three river systems, did
not invariably show similar patterns, with various elements having higher dissolved concentrations upstream. Because the concentration
of total solids increased downstream, this implied that some components of the sewage had effectively sequestered available
elements from solution and converted them to particulate material. Although the impact of pollution is clearly recognizable
in water samples collected in proximity to the anthropogenic source, there are only slight elemental accumulations in the
lower reaches of the Mahanadi River, with no accumulation in the Brahmani River. Apparently for these large rivers, discharged
effluent becomes rapidly diluted, while complexation and sedimentation further removes trace elements from the water column.
However, in the less voluminous Baitarani River, elementar enrichment near the river's mouth suggests that in this secondary
river, where dilution effects are less, the concerns over regional water quality may be more prevalent.
Received: 1 April 1995 · Accepted: 30 August 1995 相似文献
673.
STABILITY OF GRAVEL BED RIVERS BASED ON SIEVE ANALYSIS DATA 总被引:1,自引:0,他引:1
Andreas DITTRICH Institute of Water Resources Management Hydraulic Rural Engineering University of Karlsruhe Germany. 《国际泥沙研究》2001,16(2)
the or are rm me un'.ox rm as n^nAndreas mlimcrbo was - ou at the -- of Karlsruh in the las l0 pe to meq esistingwt and wt our W on tbe bo Of th6 stabmp of bo edconSsting Of graVe and stones. Sbo in the ds mOuntain wt with tyPbo sbo Of I== 0.05% tO 0.8% as well as those with distinct ~ strUCtUres and slpe of I > 4% and I Sl0% were investipe. host ot the -- were conot in the bo--. bo som Of the results that bad bo for under tw COntwcoul be eded with ealsting field data. In the followin,… 相似文献
674.
Considerable progress has been made recently in characterising the patterns displayed by the anabranches of braided rivers. However, the physical processes of sediment scour, transfer and deposition that govern the generation and evolution of anabranch channels remain largely unexplained. Direct measurement of three-dimensional flow fields and morphological evolution of the anabranches in the braided Brahmaputra–Jamuna River, Bangladesh, were undertaken to investigate the interactions between fluvial processes and anabranch morphology. These data were used to elucidate the circumstances leading to the bifurcation of a single channel, which is a topic of fundamental importance to understanding the physical processes responsible for braiding. Results indicate that division of the velocity field into multiple threads within a single channel precedes a division in the cross-sectional morphology of the channel and appears to be a necessary prerequisite for development of a bifurcation. An empirical relationship was established to discriminate between channels with single and multi-thread velocity fields, based on the depth-to-width ratio and specific energy of the flow at a representative channel cross-section. This function requires further validation, but could be used to predict the conditions under which a single channel is likely to bifurcate to produce two anabranches. 相似文献
675.
甘肃省主要河流径流时空分布规律及演变趋势分析 总被引:21,自引:0,他引:21
通过对甘肃省主要河流径流时空分布规律的分析研究,得出干旱缺水的主要原因是各河年径流丰水时段很短,一般只有2~3年;枯水时段很长,可达7~26年;祁连山区许多河流多年均值基本稳定。并预测从1998年开始至2009年,全省诸河水量从枯水年代转向平水到偏丰的年代;建议全省必须树立长期抗旱的思想,水资源利用必须进行系统分析优化配置。 相似文献
676.
R. J. Uncles 《Estuarine, Coastal and Shelf Science》2002,55(6):829
The literature on estuarine physical studies is vast, diverse and contains many valuable case studies in addition to pure, process-based research. This essay is an attempt to summarize both some of the more recent studies that have been undertaken during the last several years, as well as some of the trends in research direction and progress that they represent. The topics covered include field and theoretical studies on hydrodynamics, turbulence, salt and fine sediment transport and morphology. The development and ease-of-application of numerical and analytical models and technical software has been essential for much of the progress, allowing the interpretation of large amounts of data and assisting with the understanding of complex processes. The development of instrumentation has similarly been essential for much of the progress with field studies. From a process viewpoint, much more attention is now being given to interpreting intratidal behaviour, including the effects of tidal straining and suspended fine sediment on water column stratification, stability and turbulence generation and dissipation. Remote sensing from satellites and aircraft, together with fast sampling towed instruments and high frequency radar now provide unique, frequently high resolution views of spatial variability, including currents, frontal and plume phenomena, and tidal and wave-generated turbidity. Observations of fine sediment characteristics (floc size, aggregation mechanisms, organic coatings and settling velocity) are providing better parameterizations for sediment transport models. These models have enhanced our understanding both of the estuarine turbidity maximum and its relationship to fronts and intratidal hydrodynamic and sedimentological variability, as well as that of simple morphological features such as intertidal mudflats. Although few, interdisciplinary studies to examine the relationships between biology and estuarine morphology show that bivalve activity and the surface diatom biofilm on an intertidal mudflat can be important in controlling the erosion of the surface mud layer. 相似文献
677.
Lateral trapping in mangrove swamps is a dominant process controlling longitudinal mixing in mangrove-fringed tidal rivers. In the dry season, the effective value of the longitudinal diffusivity is increased by the trapping effect by typically two orders of magnitude, from its value in the absence of swamps. In the wet season, freshwater is trapped within the swamp and the adjoining boundary in the tidal river, for long periods following the passage of a short-lived flood. This may have important ecological implications. A fluid-mud layer appears to be created by strong tidal currents over colloidal mangrove mud. 相似文献
678.
Bankfull discharge is identified as an important parameter for studying river morphology, sediment motion, flood dynamics and their ecological impacts. In practice, the determination of this discharge and its hydrological characteristics is not easy, and a choice has to be made between several existing methods. To evaluate the impact of the choice of methods, five bankfull elevation definitions and four hydrological characterizations (determination of duration and frequency of exceedance applied to instantaneous or mean daily data) were compared on 16 gravel‐bed river reaches located in France (the catchment sizes vary from 10 km2 to 1700 km2). The consistency of bankfull discharge estimated at reach scale and the hydraulic significance of the five elevation definitions were examined. The morphological definitions (Bank Inflection, Top of Bank) were found more relevant than the definitions based on a geometric criterion. The duration of exceedance was preferred to recurrence intervals (partial duration series approach) because it is not limited by the independency of flood events, especially for low discharges like those associated with the Bank Inflection definition. On average, the impacts of the choice of methods were very important for the bankfull discharge magnitude (factor of 1·6 between Bank Inflection and Top of Bank) and duration of exceedance or frequency (respectively a factor 1·8 and 1·9 between mean daily and instantaneous discharge data). The choice of one combination of methods rather than another can significantly modify the conclusions of a comparative analysis in terms of bankfull discharge magnitude and its hydrological characteristics, so that one must be cautious when comparing results from different studies that use different methods. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
679.
680.
Julian C. Green 《地球表面变化过程与地形》2003,28(9):979-991
The precision of sampling different grain‐size percentiles in comparison to each other is of signi?cance for choosing which percentile is appropriate to characterize riverbed surface sediments. The traditional view, based on normal grain‐size distributions derived by the Wolman grid‐by‐number method, has identi?ed the median percentile as having the highest sampling precision. However, grain‐size distributions are highly variable and often fail to follow a theoretical distribution. This paper presents both theoretical and empirical techniques to determine the precision of sampling different percentiles. These methods are then applied to a range of natural distributions found in UK rivers. It is found that grains between the 66th and 91st percentiles are the most precisely sampled, with maximum precision obtained with the 73rd percentile. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献